1. Field of the Invention
The invention relates in general to clip on heat sink assemblies, and, in particular to clip on heat sink assemblies for conventional electronic packages with side projecting leads and outwardly projecting bumpers or ears to protect those leads.
2. Description of the Prior Art
Electronic devices generate heat when operated. That heat must be dissipated in some way or the electronic device will be ruined. The electronic devices, particularly chips, are often mounted in electronic packages. One form of such an electronic package which is generally used is described as a plastic quad flat pack (PQFP). A PQFP electronic package is a generally flat container in which a chip is mounted. Leads extend outwardly from the sides of the package at a location approximately midway between the upper and lower surfaces of the PQFP. These leads are small and quite easily bent, so they are protected from damage by bumpers or ears which extend outwardly from the corners of the package.
Heat is often dissipated from electronic devices by mounting finned heat radiators in heat conducting relationship with the exposed surfaces of the devices. Such heat radiators need to be firmly mounted to the electronic device or package so that heat flows by conduction from the device to the radiator. Also, the radiator must be secured so that it does not fall into contact with surrounding leads and electronic devices.
Heat radiators are generally mounted to electronic devices and packages in one of two ways. A heat-conductive adhesive may be used which, when cured, bonds the radiator more or less permanently to the package or device. Alternatively, and preferably, a spring clip such as that shown, for example, in Blomquist, U.S. Pat. No. 5,208,731 patented May 4, 1983, is used to clip the heat sink to the electronic device. Such clip mounted heat sinks or radiators are quickly and easily applied and removed. Spring clips generally extend normally downwardly along the side of the electronic device or package and engage with either the bottom of the device or the base in which it is mounted. Where conductive leads extend out of the side of a package as in the PQFP design, it is not possible to extend spring clips down along the side of the package. It had previously been generally believed that, despite its drawbacks, the only way to mount a heat sink on a PQFP electronic package was by means of adhesive. Spring clips, it was generally believed, would short out the leads.
These and other difficulties of the prior art have been overcome according to the present invention.